Two-port network for signal transmission equalization

ABSTRACT

A two-port network for use in transmission line equalizers in repeatered wide-band communication systems is disclosed. The network includes a resistive element connected between corresponding terminals of the input and output ports. A single one-port uniformly-distributed RC network is connected between the terminals of the output port. The two-port network is adapted to integrated circuit construction and may be cascaded through buffer amplifiers. Alternatively, the two-port network may form a part of a feedback equalizer. In one embodiment, the resistive element is a P-I-N diode controlled by a peak detector. In another embodiment, the two-port network is used as the feedback circuit.

United States Patent 1 Iwakami [451 Sept. 16, 1975 1 TWO-PORT NETWORK FOR SIGNAL TRANSMISSION EQUALIZATION [75] Inventor: Takuya lwakami, Tokyo, Japan [22] Filed: Feb. 5, 1974 [21] Appl. No.: 439,772

[30] Foreign Application Priority Data Feb. 9, 1973 Japan 48-16842 [52] U.S. Cl 333/18; 333/23; 333/28 R; 333/70 CR [51] Int. CI.?..H03H 7/06; H03I-I 7/16; H0311 13/00 [58] Field of Search .333/18, 23, 28 R, 70 CR; 178/71 H; 317/256; 323/74, 79

[56] References Cited UNITED STATES PATENTS 3,568,100 3/1971 Tarbox 333/28 R X 3,753,161 8/1973 lwakami 333/70 CR X FOREIGN PATENTS OR APPLICATIONS 1,185,494 3/1970 United Kingdom 333/70 CR OTHER PUBLICATIONS Hager, Network Design of Microcircuits, Electronics, Sept. 4, 1959, pp. 44 and 48.

Smith et al., Distributed Components in Printed Circuits, Proc. Electronics Component Symposium, 1956, Wash., DC, pp. 212, 213.

Tumey, Electric Filters, Pitman & Sons, Ltd., London, England, 1947, Title page and pp. 1 11, l 12.

Swart et al., A V0ltageC0ntr0lled Tuneable Distributed RC Filter, IEEE Jour. of Solid State Circuits, Aug. 1972, pp. 306, 307.

Primary Examiner-Paul L. Gensler Attorney, Agent, or F irm-Su ghrue, Rothwell, Mion, Zinn and Macpeak [57 ABSTRACT A twoport network for use in transmission line equalizers in repeatered wide-band communication systems is disclosed. The network includes a resistive element connected between corresponding terminals of the input and output ports. A single oneport uniformlydistributed RC network is connected between the terminals of the output port. The two-port network is adapted to integrated circuit construction and may be cascaded through buffer amplifiers. Alternatively, the two-port network may form a part of a feedback equalizer. In one embodiment, the resistive element is a P-I-N diode controlled by a peak detector. In another embodiment, the two-port network is used as the feedback circuit.

10 Claims, 11 Drawing Figures DETECTOR CIRCUIT PATENTEDSEPIBISYS 3,906,406

SHEET 1 0F 3 H02 g X T a I l (a) V (b) (c) ((1) mfl PATENTEB SEP I 8 I975 sum 2 0 3 FIG. 5

DETECTOR CIRCUIT FIG. 6A

TWO-PORT NETWORK FOR SIGNAL TRANSMISSION EQUALIZATION BACKGROUND OF THE INVENTION 1. Field of the Invention:

The present invention relates to a two-port network for use in a repeater for a wide-band repeatered coaxial line communication system as dummy transmission lines or constituents of variable or fixed line equalizers.

2. Description of the Prior Art A coaxial cable as a transmission medium for a communication system has a voltage transfer function C(S), which is given at frequencies above several tens of kilohertz by:

( l where S j w; j l; exp designates exponential function whose base is of the natural logarithm and given by 2.7183 (n; the angular frequency (radian/sec); a, a constant substantially determined by the material and structure of the cable; and I. the length of the cable. In order to transmit waveforms without distortion in the repeatered communication system, therefore, the line equalization for compensating for the transmission characteristic of Eq. (1) must be made at each repeater. The cable length depends on the spacing between every two adjacent repeaters, and is not always precisely constant because of the geographical and other restrictions imposed on building the repeaters. In addition, the constant a is subjected to an appreciable change with the ambient temperature variation, which causes .effects equivalent to shortening and lengthening of the cables.

In the repeatered coaxial line communication system, it is therefore necessary to suitably insert coaxial line equalizers at each of the repeaters or at least at some of the repeaters. Each of the coaxial line equalizers comprises: (i) a fixed equalizer so designed as to compensate for the cable characteristic at a fixed standard repeating distance; (ii) a set of dummy cables providing several equivalent cable lengths for electrically equalizing the tra nsmission lines for various repeater spacings; and (iii) a variable line equalizer of a sloped AGC type, for compensating for the non-uniformity of the lengths of the cables and for cancelling the shortening or lengthening effect on the coaxial cables depending on the temperature change.

Uniformly distributed RC network type equalizers have been in general and extensive use as the fixed equalizer (i) and as the dummy cables (ii), while the Bode type equalizer has been used as the variable line equalizer (iii). Various modification of these circuits are also in use. As regards these compensating circuits, further description will not be given here because they are described in detail in the US. Pat. Nos. 3,706,053 and 3,753,161 and in the technical paper entitled Variable Equalizers by H. W. Bode(B.S.T.J., 17th April, 1938, pp. 229-244, particularly p. 237). The conventional coaxial line equalizer is as a whole com plicated and difficult to miniaturize. Furthermore, the variable line equalizer (iii) is easily affected by parasitic capacitance and inductance, and therefore it is difficult to broaden its transmission band. In addition, in order to obtain a sufficiently accurate approximation of characteristic by the coaxial line equalizer, the circuit arrangement becomes unavoidably complicated. Also, an equalizer usable as the variable line equalizer has been proposed as shown in my co-pending US. Pat. Nos. 3,789,326 and 3,806,839

SUMMARY OF THE INVENTION An object of the present invention is therefore to provide a novel two-port network of a simplified circuit construction, which is for use as a dummy transmission line or as a constituent of a variable or fixed line equalizer.

The two-port network of the present invention comprises a single resistance element and a single uniformly-distributed RC network. As compared with the conventional two-port networks, it is characterized in that the circuit arrangement is simple and easy to manufacture in the form of an integrated circuit and that the equivalent cable length of the network, when used as the dummy transmission line, can be easily varied by changing the value of the single resistance element.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in detail with reference to the accompanying drawings, wherein;

FIG. 1 shows a circuit diagram of a two-port network, which is a first, principal embidiment of the present in vention;

FIG. 2 shows a perspective view of a uniformly distributed RC network constituting the embodiment;

FIGS. 3(a) through 3(d) show several modes of connection possible for the uniformly distributed RC network used as a one-port element;

FIG. 4 shows characteristic curves showing the effects of the present invention;

FIG. 5 shows a second embodiment of the present invention adapted to approximate the transmission characteristic of a long coaxial cable;

FIGS. 6A and 6B show a third embodiment of the present invention applied to a sloped AGC circuit; and FIG. 7 shows a fourth embodiment of the present invention applied to a feedback type fixed line equalizer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to FIG. 1, reference numerals 1 and 2 denote the input port; 3 and 4, the output port; 5, a resistor; and 6, a uniformly distributed RC network. The uniformly distributed RC network 6 has a distributed constant RC line in which the resistance and capacitance per unit length are uniformly distributed in the lengthwise direction By way of'example, it can be realized by a structure as shown in FIG. 2.

Referring to FIG. 2, a resistive layer 8 of a constant specific resistance is formed on one major surface of a dielectric plate 7 of a suitable width, thickness, and a uniform dielectric constant. A conductive layer 9 is similarly formed on the other major surface of the dielectric plate 7', while conductor strips 14 and 15 are disposed on the resistive layer 8. Lead terminals 10 and 12 are bonded to the conductor strips 14 and 15 respectively so as to provide a uniform current distribution in the vicinity of their bonded points. Terminals l l and 13 are connected to the conductive layer 9. (For further details, reference is made to US. Pat. No. 3,706,053).

As apparent from the structure in FIG. 2, the uniformly-distributed RC network is essentially a twoport element. Therefore, in order to use the element as a one-port element 6 of the arrangement shown in FIG.

1, four modes of connection are possible as shown in FIGS. 3(a) to 3(d). The impedances given by these modes of connection to the one-port element are as follows:

where R and C are the overall resistance and capacitance of the distributed RC network, respectively. Now if and w we have tanh i coth m= l More definitely, the errors of Eqs. (7) and (8) are only within ii% for w 2 ii) to and within 110% even for w i w... Under such conditions, Eqs. (2) and (3) can be put as being approximately equal to VR- /(C S). Quite similarly, at w 4 (o E s. (4) and (5) are approximately equal to V4R ](c S) and VRJM S) respectively.

if, in FIG. 3 (c), the length of the distributed RC network is halved and the width is doubled, the total resistance will become V4 while the total capacity remains unchanged. Therefore. the impedance becomes R1/(C S) (w 4 w r This is the same value as the impedance for the case where the terminals with the original dimensions are connected as shown in FIG. 3 (a) or 3 (h). In this manner, by appropriately setting the values of the distributed constants, all the distributed RC networks in FIG. 2 (a) 3 (d) can be given the same impedance value at frequencies above the certain value. For this reason, the one-port impedances Z( S) of the distributed RC networks are hereinbeiow represented by that of the structure in FIG. 3 (a). That is:

Z(S)=I (9) The angular frequency range in which the approximation of Eq. (9) holds veryprecisely is given by:

.. 1... l/(R c1) Here, introducing a symbol (a given by e r/i R2 1) (i2) tradlsee) then the amplitude characteristic of Eq. (I l) as indicated in decibels is as follows:

20 log I'IUwH 2(l log l +V ](w7w,,)| (rill) i ii) While, the amplitude characteristic of the coaxial cable expressed in decibels is introduced from Eq. (l):

20 |o ,.,|c w)| =-l20 0d log e] vw= -k J5me) (14) where k 20 a1 log e us it is found that the approximation error of Eq. iii) to Eq. (i4) is very small. For example, a curve 16 in Fig. 4 indicates the characteristic of Eq. (i4) at k 5.5, while a curve 17 in the same figure indicates the char acteristic of Eq. (l3) at w I (rad/sec). The approximation error is only 3:0.l7 dB at the maximum, for:

. l6) When the value of k is smaller than 5.5, the error can be further diminished. By way of example, 01,, is made 3.0 for k= 3.3, whereby the error for ca m S i (rad/- sec) can be restrained to :0. l0 dB.

The equivalent cable length of the network, when used as the dummy transmission line, can be easily varied by changing the value of the resistor 5. The variable range of the resistor 5 depends on the value of the coefficient It inherent to the coaxial cable to be equalized.

For example, when the amplitude characteristic of the coaxial cable under the condition 0 k S 5.5 must be equalized in the band-width O m S i (rad/sec). w in Eq. (l3) can be changed in the range from i (rad/- sec) to infinity, and hence the variable range of the resistance value R of the resistor 5 is given by O R S VR IC The approximation error in this case ranges between 10A? dB in the band-width 0 w 5 l (rad/- sec), and becomes maximum when k is equal to 5.5.

in this manner, the two-port network in FIG. I can be used as the dummy transmission line equivalent to the coaxial cable with the coefficient k below 5 6, with sufficient approximated accuracy (this cable cor responds to, for example, a 9.5 mm standard coaxial cable with the length of 100 I20 m, used at 400 MHz). Since the equations for detennining the three values R, R, and C of the equalizer are only two, that is, Eqs. (10) and (i2), R X C, can be arbitrarily increased to lower (0 and the lower-limit frequency can be freely lowered.

When the value of k is greater than 5 6, several twoport networks as shown in FIG. 1 are connected in cascade, as shown in FIG. 5, through bufleramplifiers l8. i9, 20 etc. by the number of necessary stages to avoid the increase in the approximation error between Eqs. (13) and (l4)- FlG. 6A illustrates a third embodiment in which the two-port network of the present invention is used as the sloped AGC type variable line equalizer. in the figure,

reference numeral 21 designates a buffer amplifier; 22, a detector circuit for detecting the peak value of the output of the amplifier 21; and 23, a variable resistance element. For this element, a P-I-N diode can be used as shown in FIG. 613. By varying the resistance R of the variable resistance element 23 in response to the output of the detector circuit 22, the equivalent variation of the coaxial cable length is automatically equalized. This will be apparent from the foregoing explanation;

FIG. 7 illustrates a fourth embodiment in which the two-port network of the present invention is applied to the feedback type fixed line equalizer. The two-port network of the present invention is employed in a feedback circuit 25 of an amplifier 24 having gain A. The voltage transfer function (8) of the circuit in FIG. 7 can be readily evaluated from the theory of the feedback amplifier, as follows:

Since the right-hand side of Eq. 20) differs only in sign from the right-hand side of Eq. (13), it will be understood that this is just the equalization characteristic for the cable amplitude characteristic of Eq. (14).

As described above, while the two-port network of the present invention has a very simple structure having a single resistance element and a single uniformlydistributed RC network, it is capable of providing a very precise approximation of the transmission characteristic of the coaxial cable. Owing to the facts that the structure is simple and that no inductance element is included, the two-port network is readily miniaturized by employing the integrated circuit technique. As a result, the influence of parasitic capacitance and inductance is minimized to permit the use at the ultrahigh frequency. Further, (1),. can be arbitrarily lowered by increasing the value of R C so as to broaden the approximation band. While the embodiments in FIGS. 6 and 7 are shown to have only one stage, it is also possible to use them in a multistage construction as shown in FIG. 5. If the resistor element 26 in the circuit in FIG. 7 is replaced with a variable resistance element, the circuit can be also used as the sloped AGC circuit.

What is claimed is:

l. A two-port network comprising;

an input port;

an output port, one terminal of said output port being directly connected to one terminal of said input port;

a lumped resistive element connected between the 20 log |(jw)| 2 20 log l other terminal of said input port and the other ter minal of said output port; and

a single one-port uniformly-distributed RC network connected between said terminals of said output port, whereby the voltage transfer function of said two-port network being given by l/(l +R/Z(S) (S=jm), where w designates angular frequency; j, \F T; R, the resistance of said lumped resistive element; and Z( S), the one-port impedance of said single oneport uniformly-distributed RC network.

2. A two-port network as recited in claim 1 wherein said single one-port uniformly-distributed RC network comprises:

a dielectric plate having a uniform dielectric constant;

a resistive layer of a constant specific resistance formed on one major surface of said dielectric plate;

a conductive layer formed on the other major surface of said dielectric plate; and

first and second conductor strips disposed on said resistive layer at opposite edges of said dielectric plate.

3. A transmission line equalizer comprising:

a plurality of two-port networks as recited in claim I;

and

a plurality of buffer amplifiers connecting said plurality of two-port networks in cascade.

4. A two-port network as recited in claim 1 wherein said resistive element is a variable resistive element.

5. A two-port network as recited in claim 4 wherein said variable resistive element. is a P-I-N diode.

6. A transmission line equalizer comprising:

a two-port network as recited in claim 4;

an amplifier connected to said output port; and

detecting means connected to the output of said amplifier for detecting the peak value of said amplifier output and adjusting the value of the resistance of said resistive element whereby the equivalent variation of the transmission line length is automatically equalized.

7. A transmission line equalizer as recited in claim 6 comprising a plurality of said two-port network, amplifier and detecting means combinations connected in cascade.

8. A transmission line equalizer comprising:

an amplifier having an input and an output; and

a two-port network as recited in claim 1 connected as a feedback circuit between said amplifier input and output, one terminal of said input and output ports being connected to the common terminal of said amplifier, said other terminal of said input port being connected to said amplifier output, and said other terminal of said output port being connected to said amplifier input.

9. A transmission line equalizer as recited in claim 8 wherein said resistive element is a variable resistive element.

I0. A transmission line equalizer as recited in claim 8 comprising a plurality of said amplifier and two-port network combinations connected in cascade.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION O PATENT NO. 3,906,406

DATED September 16, 1975 INV ENTOR(S) Takuya Iwakami It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shnwn below:

IN THE SPECIFICATION:

Column 1, line 11, after "cable" insert -usedline 20, after "2.7183" insert a semicolon same Q line, delete the semicolon after w and insert a comma Column 2, line 24, delete "embidiment" insert embodiment-- line 50, after "direction" insert a period Q Column 3, lines 37 & 38, delete /R 7(4 C S)"insert -;/R (4 C S) line 43, delete "R /(C S) w 4 w insert Q R /(C S) (w 4w line 48, delete "2(a)" ini (a)-- Column 4, line 1, after right-hand side of equation (11) insert l/(l+R/Z(S) line 7, after "m R /(R C insert -(rad/sec)- lines 9 & 9, delete "(rad/- sec) line 42, delete "0" in equation, insert -m line 46, delete "0" in equation, insert -w Column 5, line 22, delete the comma between "B" and (S) Signed and Sealed this tenth Day Of February 1976 [SEAL] Arrest.

RUTH C. MASON C. MARSHALL DANN Arresting ()jjficer Commissioner oflatems and Trademarks 

1. A two-port network comprising: an input port; an output port, one terminal of said output port being directly connected to one terminal of said input port; a lumped resistive element connected between the other terminal of said input port and the other terminal of said output port; and a single one-port uniformly-distributed RC network connected between said terminals of said output port, whereby the voltage transfer function of said two-port network being given by 1/(1 +R/Z(S) ), (S j omega ), where omega designates angular frequency; j, square root -1; R, the resistance of said lumped resistive element; and Z(S), the one-port impedance of said single one-port uniformly-distributed RC network.
 2. A two-port network as recited in claim 1 wherein said single one-port uniformly-distributed RC network comprises: a dielectric plate having a uniform dielectric constant; a resistive layer of a constant specific resistance formed on one major surface of said dielectric plate; a conductive layer formed on the other major surface of said dielectric plate; and first and second conductor strips disposed on said resistive layer at opposite edges of said dielectric plate.
 3. A transmission line equalizer comprising: a plurality of two-port networks as recited in claim 1; and a plurality of buffer amplifiers connecting said plurality of two-port networks in cascade.
 4. A two-port network as recited in claim 1 wherein said resistive element is a variable resistive element.
 5. A two-port network as recited in claim 4 wherein said variable resistive element is a P-I-N diode.
 6. A transmission line equalizer comprising: a two-port network as recited in claim 4; an amplifier connected to said output port; and detecting means connected to the output of said amplifier for detecting the peak value of said amplifier output and adjusting the value of the resistance of said resistive element whereby the equivalent variation of the transmission line length is automatically equalized.
 7. A transmission line equalizer as recited in claim 6 comprising a plurality of said two-port network, amplifier and detecting means combinations connected in cascade.
 8. A transmission line equalizer comprising: an amplifier having an input and an output; and a two-port network as recited in claim 1 connected as a feedback circuit between said amplifier input and output, one terminal of said input and output ports being connected to the common terminal of said amplifier, said other terminal of said input port being connected to said amplifier output, and said other terminal of said output port being connected to said amplifier input.
 9. A transmission line equalizer as recited in claim 8 wherein said resistive element is a variable resistive element.
 10. A transmission line equalizer as recited in claim 8 comprising a plurality of said amplifier and two-port network combinations connected in cascade. 